I would just hug your daughter and tell her to do what she believes is right. It's not her issue to "set up" her friends nor should it be. She should stay out of other people's love lives. Especially at that age, there's so much drama in young people. If the friends are really interested in one another then they'll find their own way to be together. :) A "set up" between friends seems like a potentially quick way to implode a long friendship. I'd try to focus on how your daughter feels about this and how she is affected.
It's nice to hear that your daughter and you have such an open and honest relationship. It'll serve you both well for your lives. We could take some lessons from you. :) I'm sure that you will make a good choice of words for this, because it seems you have set yourself up for being in a good place with your daughter already. Just aim to do good and not to exert too much influence on others personal lives. That would be my advise to my daughters. Focus on being the best person you can be, to others, and of course academically. Don't invest yourself in the outcome of other people's relationships because in the end you don't really have any control there. :) it's a great opportunity to learn a valuable life lesson no matter the sexuality of the people involved. This is a modern time and universal rules still apply to these same-sex relationships too. :)